The oil in the hydraulic system enters the filter from the inlet, passes through the zigzag surface of the filter element, the impurities in the oil are adsorbed on the surface of the filter material, the clean liquid is immersed in the filter element, flows out from the outlet, and the clean liquid flows into the system. Such circulation ensures the cleanliness of the hydraulic system. Bypass valves open when backpressure reaches a predetermined level. The backpressure is created as the element becomes clogged with particles. As the bypass valve opens, fluid sidesteps the element itself, flowing around it to avoid excessive and damaging backpressure, especially in return lines. Suction and return filters are sized appropriately to handle the maximum flow possible with reasonably low backpressure. larger filter have higher dirt holding capacity.